Yes, that is exactly the use case of our "user defined" transformation functions. You can define any javascript function (right now by modifying the code but will be available from the UI in the release coming next week). Inside that function you can filter/transform/enhance the event in any way you like. You can lookup your DB, call external APIs etc. You can also combine multiple events into one.
Since this whole thing runs inside your VPC, you don't have to open up your production database to 3rd party as you have to do with segment.
Happy to work with you on your use case. Please email soumyadeb@rudderlabs.com
We wrote a couple of blog posts on that.
Case Study: https://rudderlabs.com/customer-case-study-casino-game/
Transformation Details:
https://rudderlabs.com/transformations-in-rudder-part-1/
https://rudderlabs.com/transformations-in-rudder-part-2/